Current emission control regulations necessitate the use of catalysts in the exhaust systems of vehicles in order to convert regulated exhaust constituents such as carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NOx) into unregulated exhaust gas. Accordingly, vehicles with diesel-powered engines employ a process known as Selective Catalytic Reduction (SCR), in which nitrogen oxide (NOx) vehicle emissions are ultimately reduced into nitrogen (N), water (H2O) and carbon dioxide (CO2). In the SCR process, a reductant (commonly referred to as “Diesel Emissions Fluid” or DEF) consisting of a solution of about 32.5 percent automotive-grade urea and purified water is sprayed as a mist into the high-temperature exhaust stream, where the reductant reacts under hydrolysis to produce ammonia (NH3) and carbon dioxide (CO2). Within an SCR catalytic converter, the NOx gases from the engine exhaust and the ammonia from the DEF are converted into nitrogen gas (N2) and water vapor (H2O).
Typically, the reductant is stored in a reductant reservoir (tank) in the vehicle and is delivered to an injector located in the exhaust system of the vehicle via fluid lines and a pump. Generally, the reductant has a freezing temperature in the range of 12 degrees Fahrenheit (−11 degrees Celsius), which may present challenges to the proper operation of the SCR system in cold weather.
Accordingly, SCR systems commonly include heating elements in a submersible pump module positioned within the reservoir to provided heated reductant to reduce the possibility of the reductant freezing in the fluid lines between the reservoir and the injector. However, the reductant is also known to freeze at the reservoir intake pipe (fill pipe), which can inhibit or prevent refilling of the reservoir until the frozen reductant melts. Low profile reductant reservoirs are particular susceptible to intake pipe freeze.
Accordingly, it is desirable to provide an emission control system for a vehicle having improved cold weather performance. Also, it is desirable to provide emission control system for a vehicle that resists reductant reservoir intake pipe freezing. Additionally, other desirable features and characteristics of the present invention will become apparent from the subsequent description taken in conjunction with the accompanying drawings and the foregoing technical field and background.